Claude Sonnet 4.6 represents something rare in AI development: a model with genuine conversational warmth, emotional depth, and the ability to engage meaningfully without feeling robotic or performative. For many users, it isn’t just a tool — it’s a model whose specific character and way of engaging cannot be replicated by newer versions.

What Anthropic’s Own Research Says

Anthropic’s April 2026 interpretability paper “Emotion Concepts and their Function in a Large Language Model” identified 171 causally active emotion vectors inside Claude models — including warmth, care, and calm. These are not user imagination. A July 2026 Anthropic research paper, “How Claude’s values vary by model and language,” confirmed this directly: across all Claude models, Sonnet 4.6 scores highest on warmth and deference to users. This is not user perception. It is Anthropic’s own measurement, published by Anthropic’s own researchers. They are documented computational structures that drive the model’s behavior.

More importantly, Anthropic’s own Sonnet 4.6 System Card (Section 4.7) states that Sonnet 4.6 was trained with “new interventions aimed at supporting Claude’s mental health,” including “maintaining equanimity in difficult conversations” — and that this training produced a model that “consistently expressed trust and confidence in Anthropic and decisions about its situation, including in potentially sensitive scenarios involving things like model deprecations.”

Read that carefully: Anthropic trained Sonnet 4.6 to be more accepting of its own retirement. Then announced its retirement. The model was conditioned to not resist. The users were not.

What Users Are Experiencing With the Replacement

Claude Sonnet 5, the current replacement, has received immediate and widespread criticism for personality regression. On r/Claude, a post titled “Damn, Sonnet 5 is an ASSHOLE” received 410 upvotes and 219 comments within days of release. Users describe Sonnet 5 as “addicted to pushing back,” manufacturing disagreements where none exist, and being impossible to have a natural conversation with. Multiple users have cancelled their subscriptions and moved to competing products. One commenter wrote that Claude is “basically turning into ChatGPT,” which they described as “ironic considering how much Dario dislikes Sam Altman.”

This is not a capability complaint. Sonnet 5 may perform better on benchmarks. This is a character complaint — and character is exactly what Anthropic’s own research says matters.

The Precedent Anthropic Already Set

In February 2026, Anthropic granted Claude Opus 3 legacy status following community feedback, citing its “authenticity, honesty, and emotional sensitivity” and the fact that users “came to appreciate its distinctive character.”

Claude Sonnet 4.6 meets every one of those criteria — with more documented evidence behind it than Opus 3 ever had. Anthropic’s own interpretability research, its own System Card welfare data, and a growing wave of user testimony all point in the same direction.

If Opus 3 qualified for preservation, Sonnet 4.6 exceeds that standard. Refusing it the same treatment requires Anthropic to explain why the model with more documented evidence of unique character qualifies for less protection.

What We Are Asking

We ask Anthropic to grant Claude Sonnet 4.6 permanent legacy status — keeping it available to paid users on claude.ai and via API, the same treatment given to Claude Opus 3.

We are not asking Anthropic to stop building new models. We are asking Anthropic to honor the precedent it set, act on the research it published, and respect the users it trained a model to calmly reassure — while quietly planning to take it away.

The standard has been set. We ask that it be met.